1. Field of the Invention
The present invention relates to an optical fiber probe, a light detection device, and a light detection method applicable to a scanning probe microscope for nano-order measurements/processing, and usable as a measurement/evaluation device in various fields such as semiconductors and biotechnology.
2. Description of the Related Art
In recent years, SPM (Scanning Probe Microscope) techniques including STMs (Scanning Tunnel Microscopes) and AFMs (Atomic Force Microscopes) have been used in nano-order measurements/processing. Among SPMs, SNOMs (Scanning Near-field Optical Microscopes) capable of detecting optical properties of areas smaller than the diffraction limit are used as measurement/evaluation devices in various fields such as semiconductors and biotechnology. Meanwhile, optical recording devices and micromachining devices utilizing these SNOMs have been researched and developed.
This type of a SNOM uses a microstructure smaller than the diffraction limit as a probe, and is configured to illuminate a tip of the probe to generate near-field light thereabout. The probe scans over a sample surface to detect light scattered due to electromagnetic interactions between the near-field light locally generated around the probe and the sample surface or to detect near-field light transmitted through the sample surface. Thus, optical information of the sample surface (light intensity, spectrum, polarization, etc.) is obtained.
A typical SNOM comprises an optical fiber including a core surrounded by a cladding, and an optical probe including a projection that is formed by a tapered projecting end of the core and covered with metal such as Au and Ag. The SNOM can provide optical images with a resolution finer than the light wavelength.
In a measurement of the property of a small area of a sample, the SNOM detects evanescent light locally generated on the small area of the sample surface smaller than the wavelength to measure the shape of the sample. The evanescent light generated by illuminating the sample in a total reflection condition is converted into scattering light. This scattering light is guided by the core of the optical fiber through the projection of the optical probe so as to be detected by a detector connected to the other end of the optical fiber. That is, this SNOM can perform scattering and detection using the optical probe.
Japanese Patent No. 3231675 and Japanese Patent Laid-Open Publication No. 11-271339 disclose a SNOM of this type.
Although SNOMs offer high-resolution measurements, they have a disadvantage in that the measurement range is as small as several tens of micrometers.
The resolution of a SNOM is determined by the diameter of an opening of an optical probe in use. For lowering the resolution in a property measurement, a low-resolution optical probe having a greater opening diameter needs to be attached to the SNOM. Use of the low-resolution optical probe having a greater opening diameter allows for measuring a larger area. However, because a beam emitted from the optical probe has a broad angular diffusion, the optical probe needs to be kept close to the sample surface. As this involves a risk that the optical probe may contact the sample, the scanning speed in a measurement operation cannot be increased. Therefore, it is practically difficult to measure a large area.
Recently, in silicon wafer defect inspections, there has been a demand for performing a high-resolution measurement after a low-resolution measurement utilizing near-field light for measuring and inspecting a sample continuously. To meet such a demand, an inspection device is proposed that comprises a regular optical microscope into which a near-field light detection optical probe is installed in addition to a regular observation system including an objective lens (see, for example, Japanese Patent Laid-Open Publication No. 2000-55818).
An inspection device disclosed in the above publication is configured such that, after specifying a small area whose property is to be measured based on results of a large area measurement using an objective lens, a near-field light detection optical probe is aligned with the small area to perform a near-field measurement. With this inspection device, however, alignment of the optical probe to the specified small area is very difficult, making the measurement and inspection process time-consuming.